1. Field of the Invention
The present invention relates to a filter for filtering a minute volume of liquid which is operated under centrifugal force or under pressure. Filters according to the present invention are useful as filters for use in various pretreatments in clinical or chemical analyses.
2. Description of Prior Arts
In clinical analyses, a filter disk of a diameter of about 1 cm which is fixed at the bottom end of a cylindrical member has been preferentially employed for removal and concentration of protein in blood serum or plasma. However, this conventional type of a filter device requires a relatively large volume, say more than 0.5 ml of a sample liquid, while, for example, the volume of blood can be sampled from a mouse is limited to about 0.1 ml, therefore, the conventional filter device cannot successfully meet with such cases. Thus, the amount of samples to be subjected to pretreatments have been decided by the size of a semipermeable membrane attached to the bottom end of the cylindrical member. When a very small volume, say several ten microliters, of a sample is pretreated in this mode of filtration, the filter membrane must be placed at the bottom end of a very fine cylindrical member. Consequently, the effective area of filtration is necessarily reduced, hence a longer time is required by the filtration.
A hollow fiber filter for a minute volume of liquid has succeeded in overcoming the above difficulties. In this filter, a large effective area of filtration is secured in a small housing by using a hollow fiber and the filtration is performed under centrifugation. This type of filter has been proved to be advantageous in rapid filtration of a liquid sample of a minute volume, but has been still confronted with a problem that this filter cannot be applied to filtration under pressure.